From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 67A8CC43334 for ; Thu, 2 Jun 2022 16:59:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237350AbiFBQ7A (ORCPT ); Thu, 2 Jun 2022 12:59:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43518 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232622AbiFBQ65 (ORCPT ); Thu, 2 Jun 2022 12:58:57 -0400 Received: from mail-pl1-x633.google.com (mail-pl1-x633.google.com [IPv6:2607:f8b0:4864:20::633]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F39FF2A27B; Thu, 2 Jun 2022 09:58:55 -0700 (PDT) Received: by mail-pl1-x633.google.com with SMTP id w3so4962204plp.13; Thu, 02 Jun 2022 09:58:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=bpaHA6RKJwrtXGcXqeUi+P0iPjqY+qIkOSMvToigMF4=; b=YbkF3Bopk5iHZi38j/bnSLcSgcib6kts8DPsAbi7ASX7PWFeH9aWGQPR7qEvhWPyGF Bzxi9qm6V9Fd7zQU6FLI5JX6Tjz+mgDPRXaBi/jXNOjQ32wHCB/nSSdrGORlCu12XvTL CuUVhVjfZg13kXV8ZsTc+FmAZWgjaW9KmN0VB8p4Y3V7PRvlp262bqZdy2mAYTPyKlwV pqenRp2LmjuA6yQWSbE7HNltyJRkJA7XAGKcXyvVwMOzpZnAA1bxou2/TNdSZyiwgCcG GjHPKawxnP6G+vhr4BHV2jFwQZ2oj6iGeXayhYpz+fWwz2vF7OMFkxND7qOwxVHsl975 3V3w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to; bh=bpaHA6RKJwrtXGcXqeUi+P0iPjqY+qIkOSMvToigMF4=; b=GvU54Okxu1SJd4Ww6rm9UJrN175sJfwr8AbW/VYtXfLIIkAPFuEO0X+dvz4zszeRXy t76sj1/rYeytK9gtXAS3yCrgJjFsnTll0HFK8+BCa2oz6QFEGp49z83S8lmcEXF/Qq5i wGUplC2sGYjCLjpICsmF05Tb5QmNM+ZAHsfKfRfx4iChGzls1E+xifz33edVye96ftxS 6VGkJY5u/4L0ejQ6ie9Tb/c3JyzYYB89sXqcoB0W2vHpRegBfcd07VU4zk/xWu5IlGI6 Qi7Uz0kIdhBd5hs0xT6RvGI+b30pNhSdiJQ+AnXgErWqIOgyxY3yFxnei5tVMbnV4a8z gCTg== X-Gm-Message-State: AOAM532i8vPFCBD7AR73TjNrKS9KQ7fIkG/k8tjw9jfWfVueeFSZMxKh 6DBWySHEsUmz5z9yGAbk6VA= X-Google-Smtp-Source: ABdhPJwEnDVX8zzHkYAAmoExZ8oCt6O2WT1vvFEmSa4EaKqyN9tIyLWO99drw6peL7QAiDzTJtupuA== X-Received: by 2002:a17:90a:de0b:b0:1e3:33e9:6665 with SMTP id m11-20020a17090ade0b00b001e333e96665mr6168197pjv.27.1654189134784; Thu, 02 Jun 2022 09:58:54 -0700 (PDT) Received: from localhost ([2620:10d:c090:400::4:49ff]) by smtp.gmail.com with ESMTPSA id p127-20020a622985000000b0050dc76281e7sm3740687pfp.193.2022.06.02.09.58.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 Jun 2022 09:58:53 -0700 (PDT) Sender: Tejun Heo Date: Thu, 2 Jun 2022 06:58:52 -1000 From: Tejun Heo To: Waiman Long Cc: Jens Axboe , cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Ming Lei Subject: Re: [PATCH v5 3/3] blk-cgroup: Optimize blkcg_rstat_flush() Message-ID: References: <20220601211824.89626-1-longman@redhat.com> <20220602133543.128088-4-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220602133543.128088-4-longman@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Thu, Jun 02, 2022 at 09:35:43AM -0400, Waiman Long wrote: > @@ -2011,9 +2076,16 @@ void blk_cgroup_bio_start(struct bio *bio) > } > bis->cur.ios[rwd]++; > > + if (!READ_ONCE(bis->lnode.next)) { > + struct llist_head *lhead = per_cpu_ptr(blkcg->lhead, cpu); > + > + llist_add(&bis->lnode, lhead); > + percpu_ref_get(&bis->blkg->refcnt); Hmm... what guarantees that more than one threads race here? llist assumes that there's a single writer for a given llist_node and the ref count would be off too, right? Thanks. -- tejun